1. Field of the Invention
The present invention relates to a process for producing 2-formyl-1,4-butanediol by hydroformylating 2-butene-1,4-diol by reaction with hydrogen and carbon monoxide in the presence of a catalyst. 2-Formyl-1,4-butanediol can be introduced, upon hydrogenation, into 2-methylol-1,4-butanediol, which is valuable as a starting material for polymers such as polyesters, as well as medicines, and, upon oxidation, into 2-carboxy-1,4-butanediol, which is useful as a starting material for polymers such as polyurethanes.
2. Description of the Related Art
Reaction of olefinically unsaturated organic compounds with hydrogen and carbon monoxide to obtain aldehydes, called hydroformylation or oxo-reaction, is known as an industrially valuable synthesis process. For this reaction, catalysts of cobalt compounds or rhodium compounds are generally used. In particular, rhodium compounds are well known as being superior to cobalt compounds in the catalytic activity for hydroformylation and the selectivity for the resulting aldehydes. However, rhodium carbonyl is unstable and hence used in forms modified with a ligand containing phosphorous, arsenic or antimony, among which organic phosphorous compounds such as triphenyl phosphine are preferably used.
Butenediol is readily obtainable by partial hydrogenation of butynediol, which is manufactured from acetylene by Reppe reaction on a large scale. Butenediol can also be obtained by hydrolyzing diacetoxy-2-butene, which is synthesized from butadiene.
U.S. Pat. No. 3,859,369 discloses hydroformylation of butenediol by using a catalyst of rhodium or the like with a ligand of a phosphine.
It is, however, difficult to achieve a high yield in obtaining the desired compound of 2-formyl-1,4-butanediol in accordance with the process disclosed in U.S. Pat. No. 3,859,369. This is because that the reaction in this process necessarily causes 4-hydroxy-2-methylenebutylaldehyde in a considerably large amount or that the reaction itself terminates midway to cause a large amount of the starting material butenediol to remain unreacted.
While it is necessary, in order to obtain the desired 2-formyl-1,4-butanediol in a high yield, to maintain the reaction temperature at a low level, the use of a phosphine as described in this U.S.P. then results in a markedly low reaction rate. For the purpose of avoiding the above problems and achieving a satisfactory reaction rate on an industrial basis, it may be considered to use a large amount of a rhodium catalyst. Since rhodium catalysts are very expensive, their use in a large amount would be uneconomical unless they are recovered and repeatedly reused for a long period of time.
U.S. Pat. No. 4,467,116 and Japanese Patent Application Laid-open No. 123134/1982 disclose a process for the hydroformylation of olefinically unsaturated compounds which comprises the use of a rhodium catalyst modified with a phosphite that can give a very high reaction rate. This process has the advantage of achieving a high reaction rate, whereby the rhodium compound can be used only in a small amount even when the reaction is effected at low temperatures and thus the problem of economy is minimized. However, even with the use of this type phosphite to effect the hydroformylation of 2-butene-1,4-diol while maintaining a low reaction temperature, the severe problem of the reaction terminating midway at a low conversion of the starting material, although the initial reaction rate is high.